Recent advances in ultrashort high-power laser technology have prompted the rapid progress of high field science based on high power lasers. Ultrahigh power femtosecond lasers, reaching an output power over 1 PW, have been constructed and being developed in a number of institutes around the world. At GIST a PW Ti:Sapphire laser with an output of 1.5 PW at 30 fs was developed in 2012. Based on this laser facility Center for Relativistic Laser Science (CoReLS) was launched in 2012 as a research center of Institute for Basic Science. The research at CoReLS focuses on experimental and theoretical investigations of super-intense laser-matter interactions occurring in the relativistic regime. In this presentation the research program and recent research results at CoReLS will be explained.